Crop selection: Ask the cow what she needs

By Dr. Zach Sawall, Vita Plus dairy technical services
We often focus on growing crops to maximize tonnage, and we figure out how to deal with that feed once it’s in the bunk. A more economical approach is to look at what the cow needs and focus on growing forage to meet those needs.

Cow perspective
When it comes to growing the right forage for the cow, we need to understand how she utilizes forage.

Digestible starch is fairly straightforward; corn silage with a higher starch content will have more calories. It is also related to how digestible the starch is (starch kd rate). The longer corn silage is in storage, the higher its starch kd rate or the more digestible it is.

When it comes to the fiber portion, we need to evaluate the units of digestible fiber a cow can get from a forage in the first hour after she consumed it. The uNDF240 is the amount of fiber that is undigested after 240 hours and the NDF kd rate is the rate of fiber digestion per hour.

When we take the pool of potentially digestible fiber (NDF minus uNDF240) and multiply it by the NDF kd rate, we get the total units of NDF a cow can digest in the first hour after consuming it. The more NDF a cow can digest per hour, the more calories that forage provides for milk production.

Forage perspective
How do the cow’s needs translate to various forages? Let’s look at a couple of example comparisons:

• BMR versus conventional corn silage: BMR corn silage has a larger pool of potentially digestible fiber (because its uNDF240 is lower) and, thus, cows can digest more units of NDF per hour from a BMR compared to a conventional corn silage.
• Italian ryegrass versus alfalfa: Italian ryegrass ultimately produces more units of NDF digestion in the first hour compared to alfalfa because its uNDF240 content is lower.

Producer perspective
Farms are faced with higher fertilizer and seed prices, unpredictable weather, and volatile commodity markets. If we continue with the mindset of growing the most tons per acre, we may not be growing the forages that provide the best opportunity to improve margins. We need to consider how to grow the most tons of digestible fiber and starch per acre at the most economic cost relative to commodity markets.

The above discussions do not conclude that BMR is better than conventional corn silage or that Italian ryegrass is better than alfalfa. Rather, they show that farms need to consider the differences in pools of digestible fiber among various forages.

Start by looking at your current rations and cost per hundredweight of energy- or revenue-corrected milk. Determine how many tons of digestible fiber you are currently feeding per day and then determine the various crops you need to grow to produce those tons. Select varieties of alfalfa, grass, or corn that provide bigger pools of digestible fiber or starch compared to other varieties. In addition, when it comes to corn silage, planting at correct population densities to achieve maximum fiber digestibility needs to be considered.

Work with your nutritionist to critically evaluate your cow’s needs and create a forage plan that meets those needs in an economical way.

This article originally appeared in the May 25, 2022, issue of Progressive Dairy. Click here for the original article.